Abstract Analysis of sorption data of hydrocarbon vapors in polyethylene and polypropylene films using Flory-Huggins, UNIFAC. Michael-Hausslein and Flory-Rehner theories are presented. Basically two models are used, one deduced with UNIFAC and Michael-Hausslein (UNIFAC-M-H) approach and the other with UNIFAC and Flory-Rehner (UNIFAC-F-R) theory. Prediction of penetrant activity values through these theories fit quite well the experimental results with errors ranging between 4.7 and 10.8%. The mean arithmetic values of the fraction of elastically effective chain in the amorphous region are f=0.4915 and f=0.3354 for polypropylene (PP) and polyethylene (PE), respectively. The experimental results with polypropylene are correlated, establishing a unique expression to predict solubility and solubility coefficient. The dependence of solubility in polypropylene over the whole range of temperature it is also presented.